Highly Efficient Oxygen Evolution Activity of Ca2IrO4 in an Acidic Environment due to Its Crystal Configuration

We systematically characterized the perovskite-like oxides Ca2IrO4 and CaIrO3 as the oxygen evolution reaction (OER) catalysts. Compared with IrO2, universally accepted as the current state-of-the-art OER catalyst, Ca2IrO4 showed an excellent OER catalytic activity in an acidic environment, whereas CaIrO3 did not. X-ray photoelectron spectroscopy (XPS) spectra showed that the oxidation of iridium in Ca2IrO4 and CaIrO3 was slightly beyond + 4. X-ray absorption near-edge structure (XANES) spectra illustrated that the IrO6 octahedral geometric structure in Ca2IrO4 and CaIrO3 showed differences. The IrO6 octahedral is asymmetrically distorted and uniformly compressed in Ca2IrO4 and CaIrO3. Therefore, we propose that the IrO6 octahedral distortion plays an important role in the OER activities.